Many communications systems employ automatic repeat request (ARQ) techniques that allow a transmitter to confirm that data transmissions have been received successfully by an intended receiver. A typical ARQ technique involves the receiver sending acknowledgment information for each received data block, with the acknowledgment information identifying the data block being acknowledged. The acknowledgment information may include a positive acknowledgment (referred to herein as an “ACK”) indicating that reception of the data block was successful, a negative acknowledgment (referred to herein as a “NACK”) indicating that reception of the data block was unsuccessful, as well as any other appropriate acknowledgment information. For example, in an enhanced general packet radio service (EGPRS) communication system, a receiver can acknowledge receipt of radio link control (RLC) data blocks using RLC/MAC control messages (where MAC refers to medium access control), such as an EGPRS packet downlink ACK/NACK control message or a packet uplink ACK/NACK control message.
In the case of a bidirectional communications system, such as an EGPRS system, the latency associated with using separate control messages to send acknowledgment information can be reduced by including such acknowledgment information with data blocks to be transmitted in the opposite direction. For example, EGPRS supports such latency reduction through its fast ACK/NACK reporting (FANR) feature. The FANR feature allows acknowledgment information to be piggy-backed with an RLC/MAC data block sent from a receiving unit to a transmitting unit through use of a piggy-backed ACK/NACK (PAN) field. However, acknowledgment information received via a PAN field is generally less reliable than acknowledgment information received via a separate packet ACK/NACK control message. As such, a data block associated with an ACK in a received PAN field is treated by the transmitter as being only tentatively acknowledged and, thus, is associated with a tentatively acknowledged state (referred to herein as a “TENTATIVE_ACK” state) until confirmed via an appropriate ACK/NACK control message. Accordingly, under certain circumstances, an EGPRS transmitter may be required to resend blocks associated with a TENTATIVE_ACK state until the appropriate ACK/NACK control message confirmation is received, even though the blocks are likely to have been already received by the receiver.